JPH04249887A - High frequency heating type cooking device - Google Patents

Abstract

PURPOSE:To provide a high frequency output in an inexpensive constitution by means of a stable magnetron by keeping input electric current in an invertor circuit constant without using an electric current transformer. CONSTITUTION:A cumulative counter 22 in a microcomputer 21 adds or subtracts addition set values or subtraction set values determined according to a magnitude of set high frequency output and an operating condition of a magnetron 14 at constant time intervals. That is, count values of the cumulative counter 22 change while following up temperature change in the magnetron 14. Anode voltage fluctuating according to temperature change in the magnetron 14 is taken into consideration, and anode electric current is adjusted from the count values of the cumulative counter 22, and input electric current in a invertor circuit 4 is kept constant so that the high frequency output can be stabilized.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency cooking apparatus in which a magnetron is driven by a variable alternating current output of an inverter circuit.

0003

[Prior Art] This type of microwave oven converts commercial AC power into high frequency power through an inverter circuit.
There is a configuration in which the voltage is boosted via a high-voltage transformer and further increased by a voltage doubler circuit to supply power to the magnetron, thereby generating microwaves. in this case,
In general, as magnetrons perform high-frequency heating, the anode voltage gradually decreases as the temperature rises.
It has the property that the input current and high frequency output from the inverter circuit decrease.

Therefore, in order to prevent the input current from decreasing in the inverter circuit, a current transformer is provided on the input side to detect the input current, and the inverter circuit is controlled so that the input current remains constant. It is considered. That is, by keeping the input current constant in this way, it is possible to control the high-frequency heating state by the magnetron to be constant, and stable cooking can be performed.

[0005]

[Problem to be Solved by the Invention] However, implementing control with the above configuration increases costs due to the provision of a current transformer to detect the input current, so it is difficult to apply it to actual products. This would be disadvantageous in some cases. In addition to this point, since the current transformer for input current detection cannot detect abnormalities on the secondary side of the high-frequency transformer, it is necessary to add a coil for abnormality detection to the high-frequency transformer or to control the current on the secondary side. However, the cost is further increased because of the need to detect the

The present invention was made in view of the above-mentioned circumstances, and its purpose is to maintain stable cooking by keeping the input current in the inverter circuit substantially constant without providing a current transformer for detecting the input current. To provide a high frequency heating cooking device that can

[Configuration of the invention]

[0008]

[Means for Solving the Problems] The present invention provides an inverter circuit that converts commercial power into high-frequency output by controlling switching elements on and off, and a high-frequency heating circuit that includes a magnetron to which the high-frequency output from the inverter circuit is applied. , a high-frequency heating cooking apparatus comprising a control circuit that provides a control signal for turning on and off the switching element, wherein an addition setting value is added to the control circuit at predetermined time intervals during the operation period of the high-frequency heating circuit. an accumulation counter that adds and subtracts a subtraction setting value at predetermined time intervals during a stop period; and an addition value determination that calculates the addition setting value according to the magnitude of the high-frequency output of the high-frequency heating circuit and the value of the accumulation counter. and a subtraction value determining means for calculating the subtraction setting value according to the value of the cumulative counter, and determining the on-time of the switching element according to the count value of the cumulative counter. The feature is that the anode current is controlled to be substantially constant.

Further, it is preferable that the cumulative counter starts counting at the same time as the high frequency heating circuit starts its first operation after power is turned on.

0010

[Operation] According to the high frequency heating cooking apparatus of the present invention, when the power is turned on and high frequency heating cooking is started, the magnetron is oscillated by the high frequency heating circuit with a high frequency output corresponding to a predetermined input current. At the same time, the cumulative counter starts a counting operation of adding the addition setting value set by the addition value determining means at predetermined time intervals. This addition set value is changed as needed by the addition value determining means, and is set according to both the high frequency output and the current count value so that the count value corresponds to the temperature rise of the magnetron.

In other words, "the higher the high frequency output and the lower the temperature, the larger the temperature rise within a certain period of time"
Based on this principle, the addition setting value is determined so that a count value close to this value can be obtained. Then, the control circuit changes the on/off control conditions for the switching elements of the inverter circuit according to the count value of the cumulative counter based on a pre-stored program. This allows the input current to be controlled approximately constant,
The input current and high frequency output of the inverter circuit can be kept substantially constant, and a stable heating state can be maintained.

Furthermore, when the high frequency output is stopped, the cumulative counter subtracts the subtraction setting value set by the subtraction value determining means at predetermined time intervals. In this case, the subtraction setting value is changed at any time by the subtraction value determining means.
It is set according to the current count value so that the count value corresponds to the temperature of the magnetron.

That is, in accordance with the principle that ``the higher the temperature, the larger the temperature drop within a certain period of time'', the subtraction set value is determined so as to obtain a count value close to this. As a result, the count value of the cumulative counter becomes a value that substantially matches the temperature of the magnetron even when the high-frequency heating circuit is stopped.

[0014] Therefore, for example, even when heating cooking is restarted after heating cooking has been stopped and the temperature of the magnetron has not sufficiently decreased, the control circuit maintains the input current at a substantially constant level based on the count value of the cumulative counter. Can be a value. That is, no matter what state heating cooking is started, the input current to the magnetron can always be kept constant, and the high frequency output can be stabilized.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a microwave oven will be described below with reference to the drawings.

In FIG. 1 showing the electrical configuration, one terminal of a power plug 1 connected to a commercial power source is connected to an input terminal P of an inverter circuit 4 via a fuse 2 and a door switch 3a. The other terminal is connected to the input terminal Q of the inverter circuit 4 via the door switch 3b and the relay switch 5.

A short switch 6 is connected to the output sides of the two door switches 3a and 3b, and when the door of the cooking chamber is closed, the door switches 3a and 3b are turned on and the short switch 6 is turned off. It looks like this. Further, since this short switch 6 is turned on when the door is opened, the inverter circuit 4 is prevented from operating in this state.

In the inverter circuit 4, the input terminal P
, Q are connected to a full-wave rectifier circuit 7, one output terminal of which is connected to a choke coil 8, a primary coil 9a of a high-voltage transformer 9, and an IGBT (in
slated gate bipolar trans
istor ) 10 to the other output terminal. In this case, the IGBT 10 is a switching element that turns on and becomes conductive when a control voltage is applied to its gate.

Between the common connection point of the choke coil 8 and the primary coil 9a and the other output terminal of the full-wave rectifier circuit 7, and between the common connection point of the primary coil 9a and the IGBT 10 and the other output terminal of the full-wave rectifier circuit 7. A smoothing capacitor 11 and a resonance capacitor 12 are connected between them, respectively. Further, a flywheel diode 13 having the illustrated polarity is connected in parallel to the IGBT 10.

A voltage doubler circuit 15 which is a high frequency heating circuit for applying an anode voltage to the magnetron 14 is connected to the secondary side of the high voltage transformer 9. The high voltage transformer 9 has two secondary coils 9b and 9c, and the secondary coil 9b is connected via a capacitor 16 to both terminals of a diode 17 having the polarity shown. The anode of this diode 17 is connected to the cathode of the magnetron 14 via a diode 18 of the illustrated polarity, and the cathode of the diode 17 is connected to the anode of the magnetron 14 and grounded. Further, the secondary coil 9c is connected to the magnetron 14 as a cathode heater power source. magnetron 14
A current transformer 19 is interposed on the anode side of the anode to detect the anode current.

Now, the control circuit 20 is composed of a microcomputer 21 and the like, and the microcomputer 21 has an accumulation counter 22, an addition value determining means 23, and a subtracting value determining means 24. A gate signal is applied to the IGBT 10 of the inverter circuit 4 via the drive circuit 25 in accordance with the programmed program, as will be described later.

The above-mentioned cumulative counter 22 has a lower limit value set to "0" and an upper limit value set to the count value when the anode current of the magnetron is stabilized, and when these values are reached by the counting operation, The count value is prevented from changing below the lower limit value or above the upper limit value.

The microcomputer 21 receives the detection current of the above-mentioned current transformer 19 via the anode current detection circuit 26, and also receives detection signals from various sensors provided in various parts of the device (not shown). It is input via various sensor circuits 27. Further, input signals from the user's operation switches are input to the microcomputer 21 via the operation input circuit 28. Further, the microcomputer 21 outputs an energization signal to the relay coil of the relay switch 5 described above via a relay drive circuit 29, and also outputs a display signal for displaying the current cooking status etc. via a display circuit 30. .

Next, regarding the operation of the above configuration, for example,
A case where the high frequency output is set to 600W will be explained.

When the power is turned on and a cooking start signal is first inputted via the operation input circuit 28, the microcomputer 20 drives and controls the magnetron 14 by the following control.

That is, the microcomputer 20 provides an on/off signal to the IGBT 10 of the inverter circuit 4 based on the count value of the cumulative counter 22. At the same time, the cumulative counter 22 adds up the addition set value set by the addition value determining means 23 at predetermined time intervals.

In this case, since this is the first cooking start after the power is turned on, the count value of the cumulative counter 22 is zero, and the microcomputer 21 controls the anode current to the magnetron 14 until the magnetron 14 is sufficiently hot. IGB so that it is 90% of the anode current when
A switching signal is given to T10. In other words, assuming that the anode voltage will decrease as the temperature of the magnetron 14 rises, the size of the count value is relative to the value when the anode current is set to 100% when the temperature eventually stabilizes. The settings will be changed accordingly.

When a switching signal is applied to the IGBT 10 by the microcomputer 21 in this way, a large voltage is generated on the secondary side of the high voltage transformer 9.
Further, the voltage is raised to a high voltage by the voltage doubler circuit 15, and an anode voltage is applied to the magnetron 14.

[0029] Thereby, heating and cooking is started using a predetermined high frequency output. Thereafter, the count value of the cumulative counter 22 is added in accordance with the temperature rise of the magnetron 14, and each time the count value reaches a predetermined level, the microcomputer 21 sends a switching signal to the IGBT 10 to the magnetron 14. The magnitude of the anode current is 92%, 94%, 96%, 98% in order with respect to the above 90%.
%, and when the count value reaches the final level, the anode current is set to 100%.

At this time, the anode voltage of the magnetron 14 also decreases as the temperature rises, so as a result, the input current from the inverter circuit 4 is held approximately constant as shown in FIG. 5, and the high frequency output is stabilized. It is a state.

Furthermore, even when the operation of the magnetron 14 is stopped, the count value of the above-mentioned cumulative counter 22 is subtracted to a value that corresponds to the decreasing temperature. Even if the operation is started again in a state where the inverter circuit 4 is not cooled down, the input current in the inverter circuit 4 can be held substantially constant by setting the anode current according to the count value at that time, as described above.

Incidentally, as shown in FIG. 6, the change in the count value of the above-mentioned cumulative counter 22 approximately follows the actual temperature rise of the magnetron 14. Therefore, for example,
When simply adding a constant value while the magnetron 14 is operating, the input current is kept constant because it counts up linearly as shown in Figure 7 and does not respond to the temperature rise of the magnetron 14. This is difficult to do, and this embodiment has been improved in this respect.

Next, regarding the process of determining the addition set value and subtraction set value of the cumulative counter 22 for determining the switching conditions of the microcomputer 21 as described above, the principle will be briefly explained using the case of the addition set value as an example. Explain.

In this embodiment, a so-called fuzzy inference method is adopted as this method, and the magnitude of the high frequency output and the count value at that time are used as the deciding factors.

Now, the following control rules are used as a general control policy for inferring the temperature rise of the magnetron 14 based on the operating state of the voltage doubler circuit 15. In other words, the control rule is ``If the high frequency output is large and the temperature is low, the temperature rise within a certain period of time will be large.'' According to this control rule, the wattage of high-frequency output is divided into three membership levels, X0, X1, and X2, as shown in Figure 2, corresponding to the three grades of "high,""medium," and "low." The current count value of the cumulative counter 22 is expressed as a function, and the current count value of the cumulative counter 22 is expressed as three membership functions Y0, Y1, and Y2 as shown in FIG. Let us express it as Next, set the size of the addition setting value to be determined as "large", "medium", or "small".
For the three grades, Z0, Z1,
It is shown by three membership functions of Z2.

Now, for example, the wattage of the high frequency output is 600W, and the current count value of the cumulative counter 22 is 4.
The process of determining the addition setting value when the value is 00 will be described. That is, first, in FIG. 2, when the values of each function at 600 W are determined, they are: X0=0, X1=0.3, and X2=0.7. next,
In FIG. 3, the values of each function when the count value is 400 are determined as follows: Y0=0, Y1=0.7, Y2=0.3.

Based on these values, membership functions Z0, Z1, and Z2 for determining the addition setting value are derived from the rule table shown in Table 1. This reflects the control rule described above, and is determined by the correlation between the grade of the high frequency output and the grade of the current count value.

[0038]

[Table 1]

From Table 1, Z0 is Z0; (X0, Y0), (X0, Y1), (X1, Y0
), but the method of determination is that the one with the smaller value among the elements in each set is taken as the value of that set, and the largest value of those three sets is set as Z.
It is set to 0. Therefore, in this case, Z0; (0, 0), (0, 0.7), (0.3
, 0), the value of each pair is "0", and Z0=
It is 0.

[0040] Similarly, when Z1 and Z2 are found based on the combinations shown in Table 1, Z1; (X
0, Y2), (X1, Y1), (X2, Y0)
; (0, 0.3), (0.3, 0.7), (0
．． 7, 0.3) ; 0
, 0.3, 0.3

Therefore, Z1=0.3.

Regarding Z2, Z2; (X1, Y2), (X2, Y1), (X2,
Y2); (0.3, 0.3), (0.
7, 0.7), (0.7, 0.3)
; 0.3, 0.7, 0.3

Therefore, Z2=0.7, and summarizing the above results, (Z0, Z1, Z2)=(0, 0.3, 0.7
).

Next, by applying these values to the membership function shown in FIG. 4, the area shown by diagonal lines in the figure is obtained. Then, by finding the center of gravity G of the figure indicating this hatched area and drawing a perpendicular line to the x-axis, the desired addition setting value can be obtained.

[0043] Thereafter, by calculating the addition setting value at any time using the same procedure, the addition setting value of the cumulative counter 22 while the magnetron 14 is operating is changed.
A change in the count value as shown in FIG. 6 is obtained, which approximately corresponds to the temperature rise of the magnetron 14. In addition, in this case, when the anode current of the magnetron 14 becomes stable,
The count value of the cumulative counter 22 has also reached its upper limit, and no further counting operation is performed.

Although detailed explanation will be omitted here, the subtraction setting value for the cumulative counter 22 while the magnetron 14 is stopped is also determined by the subtraction value determining means 24 based on the above-mentioned fuzzy reasoning. and,
In this case, as a control rule, the subtraction set value is set according to the principle that ``If the temperature is high, the temperature drop within a certain period of time is large.'' Also,
In this case, when the temperature of the magnetron 14 becomes sufficiently low, the count value of the cumulative counter 22 returns to "0", and no counting operation is performed thereafter even if the stop time continues. .

According to this embodiment, the addition value determining means 23 and the subtraction value determining means 24 determine the addition set value and the subtraction set value by fuzzy reasoning, and the count value of the cumulative counter 22 is determined by the count value of the magnetron 14. The control circuit 20 determines the switching conditions of the IGBT 10 so as to set the anode current of the magnetron 14 according to the count value, so that the input current of the inverter circuit 4 is changed to a value corresponding to the temperature change. It is possible to easily control the high frequency output to a substantially constant level without providing a transformer, and it is possible to stably control the high frequency output.

Furthermore, according to this embodiment, the cumulative counter 2
Since the counting operation in step 2 is performed at the same time as the first high-frequency output operation starts after the power is turned on, the temperature of the magnetron will be followed regardless of whether the magnetron 14 is in operation or stopped after the user turns on the power. Since the count value of the cumulative counter 22 can be changed by changing the count value of the cumulative counter 22, the input current in the inverter circuit 4 can always be kept constant.

In the above embodiment, the addition setting value and the subtraction setting value are determined by fuzzy inference, but the invention is not limited to this, and each time the count value reaches a predetermined boundary value, the addition setting value or the subtraction setting value is determined. may determine the subtraction setting value.

[0048]

According to the high-frequency heating cooking device according to claim 1, the control circuit is provided with an accumulation counter, an addition value determining means, and a subtraction value determining means, and the anode voltage of the magnetron is adjusted according to the operating state of the high-frequency heating circuit. To solve this problem, the anode current of the magnetron is set by performing a counting operation using a cumulative counter so that the count value corresponds to the temperature of the magnetron. Therefore, there is no need to install a current transformer on the input side, and it can be done at low cost. This provides an excellent effect in that the input current can be held constant and a stable high-frequency output state can be achieved.

According to the high frequency heating cooking apparatus according to the second aspect, since the counting operation of the cumulative counter is performed simultaneously with the start of the first high frequency output operation after the power is turned on,
After the user turns on the power, the count value of the cumulative counter can be changed to follow the temperature of the magnetron regardless of whether the magnetron is in operation or stopped, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is an electrical configuration diagram showing one embodiment of the present invention.

[Figure 2]
Explanation diagram of membership function of high frequency output

[Figure 3] Explanatory diagram of membership function of count value

[Figure 4] Explanatory diagram of membership function of addition value

[Figure 5] Characteristic diagram showing the transition of input current with respect to magnetron operating time

[Figure 6] Diagram explaining the time transition of the count value of the cumulative counter

[
Figure 7: Diagram equivalent to Figure 6 when no cumulative counter is used

[Explanation of symbols] In the drawing, 4 is an inverter circuit, 5 is a relay switch, and 7 is an inverter circuit.
is a full-wave rectifier circuit, 9 is a high-voltage transformer, and 10 is an IGBT (
14 is a magnetron, 15 is a high frequency heating circuit, 19 is a current detection coil, 20 is a control circuit,
21 is a microcomputer, 22 is an accumulation counter, 2
3 is an addition value determining means, 24 is a subtraction value determining means, and 26 is an anode current detection circuit.

Claims (2)

[Claims] 1. An inverter circuit for converting commercial power into high-frequency output by controlling on/off of a switching element, a high-frequency heating circuit having a magnetron to which the high-frequency output from the inverter circuit is applied, and a high-frequency heating circuit for turning on/off the switching element. In the high-frequency heating cooking apparatus, the control circuit adds an addition set value at predetermined time intervals during the operation period of the high-frequency heating circuit, and subtracts the set value during the stop period. an accumulation counter that subtracts the value at predetermined time intervals; an addition value determining means that calculates the addition setting value according to the magnitude of the high-frequency output of the high-frequency heating circuit and the value of the accumulation counter; and a subtraction value determining means for calculating the subtraction setting value, and controlling the input current from the inverter circuit to be substantially constant by determining the on-time of the switching element according to the count value of the cumulative counter. A high frequency heating cooking device characterized by: 2. The high-frequency heating cooking device according to claim 1, wherein the cumulative counter starts counting at the same time as the first operation of the high-frequency heating circuit starts after power is turned on.